Car radio says ipod touch has "No Music" when pulged in when it has over 300 songs

I have never had a problem with my ipod playing through my radio until just a couple days ago. The radio does show that the ipod is pluged in but it says that there is no music on my ipod when there are actually hundreds of songs on it. I have tried pulging a friends ipod touch into my radio and theirs works so it is my ipod that isn't working right. Has anyone else had this problem or have any ideas on how to fix it.